1. Field of the Invention
This invention relates generally to a syringe for the controlled discharge of viscous materials and, more particularly, to a syringe for the controlled discharge of dental materials.
2. Description of the Prior Art
A syringe of the prior art is described, for example, in the product information published by Heraeus Kulzer GmbH "Charisma-Inlays--Gewinn durch Perfektion und Asthetik" [Charisma Inlays--Profit from Perfection and Appearance] (31292/D 125 sK dt./WPR 12 12 200). These syringes, which contain the viscous dental materials sold under the name "Charisma" (Charisma is a registered trademark of Heraeus Kulzer GmbH), have a cartridge which holds the dental material. This cartridge is tapered on the outside circumference of its discharge end to form a material discharge nozzle which is closed by attaching a cap. In an end of the cartridge opposite the discharge end, a rotary piston is inserted. The rotary piston is in contact on one end with a sleeve-shaped stopper which is in contact with the viscous material in the cartridge. The rotary piston is provided with a threaded portion which is guided in a bearing in the form of a nut. To discharge the dental materials from the cartridge, the cap is removed from the cartridge and the rotary piston, which has a handle on its end, is twisted into the cartridge. The stopper is thus pushed toward the discharge end of the cartridge and applies pressure to the material. The syringes described above have been used successfully for years.
Another syringe for the discharge of viscous materials is disclosed in U.S. Pat. No. 3,581,399. This syringe has a removable tip or nozzle which is curved in the shape of a thin channel for controlled application of dental material to one spot on a tooth to be worked on. This tip is screwed onto the end of the cartridge or, in another embodiment, is swung into place and locked. German Application No. 42 00 044 A1 discloses a dental cartridge for the discharge of multi-component material for dental fillings which is inserted in a syringe and is operated by a lever. This syringe has a pistol-like adapter into which the cartridge containing the dental material is inserted. German GM 78 37 177 discloses a syringe for the direct application of dental filling material where the container which contains the filling material is configured as a collapsible capsule inserted into the cartridge. U.S. Pat. No. 3,900,954 discloses a syringe which is similar to the syringe disclosed in U.S. Pat. No. 3,581,399. A piston having a projecting tip is inserted under some friction into a cartridge. The tip of the piston presses into a sleeve-shaped part in which the dental material is located. The small, sleeve-shaped part is attached to the end of the cartridge and forms the discharge tip or nozzle for the material.
The cartridges described above which hold the dental materials are generally filled from the rear end, i.e., the end which is opposite the discharge nozzle. After the cartridge has been filled from the rear, the above-mentioned sleeve-shaped stopper is pushed into the open filling end of the cartridge until it is in contact with the loaded material. The rotary piston then presses against the stopper to discharge the material. Such cartridges which hold the dental material have a slight conicity on the inside, having a larger diameter on the side from which the dental material is filled and from which the stopper is inserted. The conicity is necessary for removing a workpiece after forming the cartridge by injection molding. Due to this conicity, the stopper is in contact with different tension in the axial direction of the cartridge against the inside wall of the cartridge as it moves from one end of the syringe to the other. There can be problems involving leaks in the cartridge, especially with low-viscosity materials. If a stopper is used which provides a tighter seal at the transition to the inside wall of the cartridge, after the process of filling the cartridge with material and insertion of the stopper, an air pocket remains between the material and the stopper which cannot escape. To counteract this problem, such stoppers were provided with a hole in the center and a drive spindle having a mandrel was provided to close the hole. After discharge of material from the cartridge, the pressure was removed from the stopper by retracting the rotary piston. However, if the rotary piston was twisted too far out of the syringe, the mandrel was necessarily pulled out of the hole in the stopper thus exposing the material in the cartridge to the atmosphere. This could result in a hardening of the material or a change in the characteristics of the material. It is precisely in the field of dentistry that very different materials must be inserted in such syringes or application instruments, including materials which polymerize when exposed to light or heat.
An object of the present invention is to design a syringe for the discharge of a controlled amount of viscous materials, in particular dental materials, which makes it possible to fill the syringe or its cartridges without the problem of an air pocket remaining between the dental material and the stopper, and which also makes possible a mechanical filling and closing of the cartridge.